1. Technical Field
The present invention relates to a recombinant Escherichia coli (E. coli) capable of producing D-xylonic acid from D-xylose and a method for producing D-xylonic acid using the same. More particularly, the present invention relates to a method for engineering E. coli capable of producing D-xylonic acid from D-xylose by disrupting the genes responsible for the metabolism of D-xylose and D-xylonic acid in wild type E. coli, and introducing a necessary gene originating heterologous bacteria, and to a method for producing D-xylonic acid from D-xylose using the engineered E. coli by the method.
2. Description of the Related Art
It is now commonly accepted that the world must shift from dependence upon fossil fuels to biomass-based fuels to combat global warming. Numerous scientists have devoted themselves to biofuel research. Compared with biofuels, research on bio-sourced chemicals and materials traditionally derived from fossils has not attracted much interest until the last decade. Biomass processing has come to the forefront of both biological and chemical engineering research.
To support the campaign on the integrated conversion of biomass, the US Department of Energy (DOE) identified 30 chemicals which could be used for the productions of high value-added chemicals in 2004. As one of the top 30 value-added chemicals, D-xylonic acid has found applications in many fields. For example, it has been utilized as a substrate for biosynthesis of 1,2,4-butanetriol. Further, it has been known that D-xylonic acid can be used as a concrete additive which improves concrete dispersion. In addition, D-xylonic acid has been reported in the fields of foods, pharmaceuticals and agriculture.
D-xylonic acid can be produced from D-xylose by microbial conversion. Bacteria such as Pseudomonas, Gluconobacter and Caulobacter are capable of producing dehydrogenase for converting D-xylose to D-xylonolactone, which can be hydrolyzed naturally or by an enzyme to produce D-xylonic acid.
D-xylose dehydrogenase is also found in the fungus Hypocrea jecorina, but its function reminas unclear. Recently, two recombinant yeast strains have been constructed aiming to produce D-xylonic acid from lignocellulosic hydrolysates.
But so far, no commercial production method of D-xylonic acid has been established. Reasons are either because bacteria strains produce many other oxidizing enzymes resulting in the conversion of other sugars present in lignocellulosic hydrolysates or because the engineered yeast strains have low D-xylonic acid accumulation rate and yield. In addition, high cost of peptone and yeast extract as nitrogen sources in the media is generally uneconomical for industrial scale production of D-xylonic acid.